Slides 13: homeostasis

Homeostasis

active process of maintaining a relatively stable, balanced internal environment

Thermoregulation

active process of closely regulating body temperature around a set value

endotherm

generate most of their own heat through internal processes - metabolism and muscular activity

ectotherm

get most of their heat from the environment

Both actively regulate body temperature, but ectotherms do so by

behavior only and not physiological (or internal) processes

2 advantages to endotherms

independence from environmental conditions and improved oxygen use capacity (sustains greater muscular activity)

Deviation from a desired value, the set point, results in

compensatory action

Most systems have more tolerance than a simple set point; generally, there is a set zone which refers to

the range of tolerance in a system

Receptors in the skin, body core, and hypothalamus detect temperature and transmit that information to the

spinal cord, brainstem, and hypothalamus

preoptic area POA of the hypothalamus is important area for

thermoregulation

Behavioral regulation of temperature uses three strategies:

1. Change exposure of the body surface, 2. Change external insulation, and 3. Change surroundings

If exposed to bacteria, iguana will create a "Fever" by

moving toward a heat source (fever helps them kill off the bacteria)

animals lick skin since evaporating saliva cools the blood which

then circulates throughout the body

intracellular compartment

The fluid contained within our cells; where most of our water resides

extracellular compartment

The fluid outside our cells

The extracellular compartment is divided between the

interstitial fluid (the fluid between cells) and blood plasma (the protein-rich fluid that carries red and white blood cells)

aquaporins

specialized protein channels that move water in and out of the cell

Osmosis

passive movement of a solvent (the liquid) to move through a membrane in order to equalize the concentration of solute (molecules of a substance)

Osmotic pressure is the physical force that

pushes or pulls water across the membrane

Osmolality

is the number of solute particles per unit volume of solvent

isotonic salt solution is about

0.9% (physiological saline) and is the same as in mammalian fluids

hypertonic solution

has more salt than an isotonic solution

hypotonic solution

has less salt than an isotonic solution

If cells are surrounded by saltier solutions (that is, a hypertonic solution), they will

lose water

If they are surrounded by less salty solutions (a hypotonic solution),

water will push into the cell

if excessive, this movement can

damage or even kill cells

Osmotic thirst is stimulated by high

extracellular solute concentration

hypovolemic thirst is stimulated by

reduced extracellular volume

osmosensory neurons in the hypothalamus response to

changes in osmotic pressure as water is drawn out of cells by osmosis

aldosterone

a steroid hormone, is released from the adrenal gland in response to thirst signals

aldosterone stimulates the kidneys to conserve

Na+ , which aids water retention

If these physiological processes aren’t enough, your body will stimulate

behavioral processes (via the circumventricular organs) to get you to drink water to remedy the thirst

circumventricular organs lie in the walls of the

ventricles where the neurons can monitor salt and hormones in the blood

Hypovolemic thirst is triggered by loss of

water volume

Barorecptors

in major blood vessels and the heart detect the drop in blood pressure

The process of digestion—breaking down food—is controlled by the nervous system, which also

anticipates future requirements

glucose

principal sugar used for energy

glycogen

is a complex carbohydrate, made by the combining of glucose molecules, stored for a short time in the liver and muscles

Glycogenesis

is the process of converting glucose to glycogen, regulated by the pancreatic hormone insluin, released by beta cells in the pancreas

Glucagon

another pancreatic hormone released by alpha cells in the pancreas, mediates glycogenolysis—conversion of glycogen back into glucose when blood glucose levels drop

lipids

(or fats) for longer-term storage, are deposited in adipose tissue

Under periods of prolonged food deprivation, gluconeogenesis kicks in to convert fat and proteins to

glucose and ketones (which can also be used by the body and brain)

Glucose transporters span the

cell membrane and interact with insulin to bring glucose into the cell

the 3 mechanism that trigger insulin release

cephalic, digestive, and absorptive

cephalic phase

The sensory stimulus of food evokes insulin release, in anticipation of glucose

digestive phase

Food causes gut hormone release, which stimulates the pancreas to secrete insulin

absorptive phase

Glucodetectors in the blood and liver detect glucose and signal the pancreas to release insulin

Diabetes mellitus is caused by

failure of insulin to induce glucose absorption

Type 1 (juvenile-onset) diabetes mellitus the

pancreas doesn’t produce insulin

Type 2 (adult-onset) diabetes is

primarily a consequence of reduced sensitivity to insulin

No single brain region has control of appetite, but the hypothalamus is important for regulation of:

Metabolic rate, food intake, and body weight

Ventromedial hypothalamus (VMH) is a

satiety center

Lateral hypothalamus (LH) is a

hunger center

The arcuate nucleus of the hypothalamus is also critical, and is key in

integrating peptide hormone signals from the body

Ghrelin hormone

synthesized and released by endocrine cells of the stomach; reaches high levels before eating and drops off after eating; works as an appetite stimulant

Pyy3-36 hormone

released by intestinal cells; reaches high levels after eating and works as an appetite suppressant

POMC neurons

act as satiety neurons when activated, inhibiting appetite and increasing metabolism

NPY neurons

act as hunger neurons, stimulating appetite and reducing metabolism when activated

Fat cells release leptin into the blood stream to provide information to the brain about

long term energy reserves

Defects in leptin production or sensitivity give a false reporting of body fat, causing animals to

overeat